Robots are widely used in different types of industrial applications, usually in such applications in which accuracy plays an important role and the same operations are continuously repeated. An example of such an operation is the manufacturing of circuit boards where the robot is equipped with an applicable gripping element, which grips the component and places it accurately to the circuit board for the next steps in the production.
The requirements for robots vary according to the environments they are used in. A specific environment is one where heavy loads are lifted and the robots are prone to shocks, like bangs and knocks, and the robots are working under unclean conditions.
One such environment is the waste industry, wherein waste is sorted e.g. from a conveyor belt. Robots are programmed to collect and recycle the waste according to characteristics of the waste. It is clear that sorting waste is not an easy task, not only due to the fact that the waste items vary in mass and shape, but also because the flow of the waste on the conveyor belt varies constantly. In this kind of sorting one requirement for robots, in addition to speed, is that the robots must not be vulnerable to shocks during the operation. The cost of idle time of an automatic waste sorting station is significant and thus it is desirable to make arrangements to minimize the effects of expected shocks during the operation.
The structure most vulnerable for shocks in robots is typically the tool, e.g. a gripper. The items on the conveyor belt vary in size and weight and may shift or roll during the operation. Collisions with items on the conveyor or the inertia of collected items may cause shocks to the robot. Furthermore, multiple robots can be deployed around the conveyor belt and two or more robots or their carried loads of unknown shape may collide for any reason, causing serious damage to the robots.
There are several prior art methods for preventing such damage to robots. Typically these are either structural arrangements such as yielding or breaking parts, or operational methods for preventing the damage, e.g. recognizing a possible collision by utilizing some sort of sensor arrangement.
In such structural arrangements parts of the robot, for example an articulated robot arm, are arranged to be at least partly flexible. This is achieved e.g. with choice of material within the arm. For example some elastic material can be arranged between two parts, e.g. an arm and a gripper, which allows the parts to bend in relation to each other in a shock situation. Another example are spring based arm solutions, which are also designed to minimize possible damage in case of shock. A third category of prior art solutions for preventing damage are structures that comprise parts which yield or break when a predetermined force is exceeded in a shock situation.
An example of operational methods for preventing damage, according to prior art solutions, are arrangements where the operation of the robot is monitored with sensors and, if a damaging situation is detected, altered to avoid damage, e.g. by stopping the robot.
One example of absorbing shocks in robotic environment is disclosed in a publication U.S. Pat. No. 7,327,112 B1. The publication discloses a tumbling robot in which a control system coordinates the action of multiple legs of the robot to cause the robot to tumble in any direction. The legs are coupled with tension wires that hold the robot in shape but also absorb the shock of the legs contacting the ground when the material of the wires is optimally selected.
Another example of suspension mechanism in the robotic area is disclosed in a publication U.S. Pat. No. 5,116,190. The publication introduces a cable suspension compliance mechanism which is to be implemented between two plates and the suspension mechanism comprises suspension cables, stiffeners and tensioning cables. It is possible to adjust the level of suspension by controlling the stiffeners. This enables the utilization of the structure in positioning of a gripping element of a robot so that an article can be optimally gripped.
Some of the drawbacks of the prior art solutions are that they are expensive to implement, e.g. detector based operational methods, or they are difficult to implement in robots which are configured to operate in challenging environments, such as waste sorting facilities. Moreover, prior art solutions based on breaking parts, e.g. clamps, cannot be used in environments, where it is basically impossible to let the whole system idle while the robot is repaired. Also, due to the complexity of the prior art solutions, the repairing takes a long time, which again is not acceptable in e.g. robotics solutions where idling of the system causes significant costs to the operator.